As the Polymer Electrolyte Membrane of this sort, a mixture of acidic perfluoro polymer that have acidic groups with basic polyethylene oxide polymer is proposed (for instance, Japanese Patent Application No. 10-249463 etc.). This electrolyte membrane is formed using a mixed solution made by mixing a solution of acidic perfluoro polymer that have acidic groups with a solution of basic polyethylene oxide polymer, and is reported to show favorable proton conductivity in a high-temperature low-humidity state.
As another Polymer Electrolyte Membrane, a substance made by immersing a basic polymer into phosphoric acid is proposed(for instance, Published Japanese Translation of PCT Application, JP-T-11-503262 etc.). This electrolyte membrane is also reported to show favorable proton conductivity in a high-temperature low humidity state.
The existence of water is inevitable when the proton conduction is performed by the migration of ionized proton hydrate, and at the same time, the favorable proton conductivity can not be obtained at a temperature exceeding the boiling point of water. In consideration of these disadvantages, the conduction with the ionized proton is performed in a manner excepting the hydration process. The term “a high-temperature low-humidity state” is used to describe a state in which the temperature exceeds the boiling point of water with the relative humidity is less than 100%.
However, in order to achieve high performance of a fuel cell, further improvement in proton conductivity has been required for the Polymer Electrolyte Membrane which is used as an electrolyte membrane. In addition, the latter Polymer Electrolyte Membrane has a disadvantage that the proton conductivity is lowered with the use of the electrolyte membrane.